Question

Let `veca=2hati+hatj-2hatk` and `vecb=hati+hatj`. If `vecc` is a vector such that `veca.vecc=|vecc|,|vecc-veca|=2sqrt(2)` and the angle between `vecaxxvecb` and `vecc` is `30^(@)`. Then `|(vecaxxvecb)xxvecc)` is equal to
A. `2/3`
B. `3/2`
C. `2`
D. `3`

Answer 1

Correct Answer - B
We have `vecaxxvecb=2hati-2hatj+hatk`
`:.|(vecaxxvecb)xxvecc|=|vecaxxvecb||vecf|sin30^(@)=3/2|vecc|`
Now,
`|vecc-veca|=2sqrt(2)`
`implies|vecc-veca|^(2)=8`
`implies|vecc|^(2)+|veca|^(2)-2(veca.vecc)=8`
`implies|vecc|^(2)|9-2|vecc|=8`
`implies|vecc|^(2)-2|vecc|+1=0implies|vecc|=1`
Hence `|(vecaxxvecb)xxvecc|=3/2`